Pull up vinyl floor or leave it down?

I have vinyl flooring over luan (1/8 or 1/4", not sure which). I want to do porcelain tile.

I've talked with a few contractors about this. The first two didn't say a word about going directly over the vinyl with the backerboard, yet the third is insisting that I rip the vinyl up or I may have problems. My floor doesn't squeak or have any issues that I can find.

Pull up vinyl floor or leave it down?

Zinger,
You got one shot to have the job done right. I am not one to cover things up and make bigger problems down the road for the next guy. The installer that wants to get rid of the luan and vinyl is giving you good advice. This is all dependent on what's underneath as Jazman stated. I personally wouldn't lay the tile over the vinyl/luan. I don't want to chance something going wrong later on when I had the chance to correct it up front.
Mike Hawkins